1. Field of the Invention
The present invention relates to a control system for a hybrid vehicle which can appropriately respond to a request of a driver to assist an engine output by an electric motor.
This application is based on Japanese Patent Application Nos. Hei 11-218218, and Hei 11-232027, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, hybrid vehicles which carry electric motors as power sources for driving the vehicles in addition to engines are known. In the conventional hybrid vehicles, there are parallel hybrid vehicles which use motors as assisting driving sources for assisting the output from the engines. The parallel hybrid vehicle assists the output from the engine by the motor when the vehicle accelerates, charges a battery by deceleration regeneration when the vehicle decelerates, and performs various controls, to respond to the driver""s demand while maintaining the remaining charge of the battery (as disclosed in Japanese Unexamined Patent Application, First Publication Hei 7-123509).
The determination as to whether to require the assistance depends on whether the opening state of a throttle exceeds a predetermined threshold value. When it exceeds the threshold value, the motor is activated to assist the output from the engine.
In the hybrid vehicle, a gasoline engine takes various measures to improve fuel consumption by, e.g., storing the thermal energy discharged from a brake unit as regenerated energy in the battery. To further improve fuel consumption, for example, a gear shift design been developed herein the gear ratios are made high enough such that the vehicle can travel at a low engine speed.
However, a vehicle with high ratio gears may not accelerate as the driver expects, for example, when a driver releases an accelerator pedal before a curve and accelerates the vehicle at the end of the curve. This decreases the commercial value of the vehicle.
In a vehicle with the high ratio gears, the gear ratio of the first gear is normal to guarantee the torque required to start the vehicle, while the gear ratio of the second gear is spaced much higher. Therefore, the engine speed suddenly varies when the gear is shifted up to second gear, and accordingly a sudden variation may be caused in the driving force.
While the conventional hybrid vehicle assists the output from the engine by the motor according to the driver""s intention to accelerate the vehicle, there are various types of the driver""s intention, depending on the driving conditions. For example, the driver may wish to accelerate continuously, to accelerate only in a short period of time at the time of starting, or to accelerate instantaneously at the time of a shift-change action.
Accordingly, the conventional vehicle cannot sufficiently respond to the driver""s demand simply by judging the presence or absence of the driver""s intention to accelerate and performing the fixed assistance by the motor.
It is therefore an object of the present invention to provide a control system for a hybrid vehicle which can improve its acceleration performance and can shift up smoothly.
It is another object of the present invention to provide an assistance control system for a hybrid vehicle which can appropriately respond to a driver""s assistance request.
In a first aspect of the present invention, the control system is provided for a hybrid vehicle with an engine (E) for outputting a driving force, a motor (M) for generating a force for assisting the output from the engine, and a power storage unit (3) for supplying a power to the motor and for storing energy regenerated by the motor when the vehicle decelerates. The control system comprises: an assistance determining device (S125, S136) for determine whether to assist the output from the engine by the motor, depending on the driving condition of the vehicle; a first assistance amount determining device (S239) for determining a first assistance amount, depending on the driving condition of the vehicle, when the assistance determining device determines to perform the assist; a second assistance amount determining device (S401) for determining a second assistance amount (SCRAST), when a driver""s intention to accelerate the vehicle exceeds a predetermined standard; and an assistance control device (1) for driving the motor to assist the output from the engine, based on the first assistance amount when a driver""s intention to accelerate the vehicle does not exceed a predetermined standard, and based on the second assistance amount when the driver""s intention to accelerate the vehicle exceeds the predetermined standard.
According to the first aspect of the invention, the assistance control device drives the motor to assist the output from the engine, based on the second assistance amount depending on e.g., the engine speed, when the driver""s intention to accelerate the vehicle exceeds the predetermined standard. Thus, the assistance by the motor can be responsive to an instantaneous assistance request by the driver. Even if a turning vehicle decreases the engine speed to an idle state and accelerates after turning, the acceleration is improved, and the commercial value of the vehicle is increased. Even when in an MT vehicle the differences in the ratios between the first and second gears, and between the second and third gear ratios, the variation in the output is decreased when shifting the gear up. Therefore, when the gear ratios are set high to improve fuel consumption, sufficient acceleration and a smooth shift-up action of the gear can be ensured.
In a second aspect of the present invention, the control system for a hybrid vehicle further comprises: an assistance time determining device (S305) for determining a period of time to maintain the assistance based on the second assistance amount; and an assistance amount gradual changer (S405, S408, S409, S229, S230, S231) for gradually increasing the present assistance amount to the second assistance amount at the beginning of the period of time set by the assistance time determining device, and for gradually decreasing the second assistance amount at the end of the set period of time.
When the driver wishes to accelerate the vehicle, the present assistance amount is gradually increased to the set assistance amount in the time of period set by the assistance time determining device, so that the acceleration is made smooth and comfortable, as compared with the case when suddenly increasing the assistance amount.
Further, at the end of the assistance time set by the assistance time determining device, the assistance amount is gradually decreased so that the vehicle can smoothly return to the normal state (in which F_MASTSCR=0), as compared with the case when suddenly decreasing the assistance amount.
In a third aspect of the present invention, the control system for a hybrid vehicle further comprises a driver""s intention determining device (S304, S308, S309) for determining that the driver""s intention to accelerate the vehicle exceeds a predetermined standard, when a throttle opening is above a predetermined value and a variation in the throttle opening state is above a predetermined value.
When the accelerator pedal is depressed significantly and instantaneously, the driver""s request of the assistance different from the normal assistance can be clearly detected. The variation in the degree of throttle opening may be replaced with a variation in the vehicle speed.
In a fourth aspect of the present invention, the assistance determining device comprises: a starting assistance determining device (S1251, S1258) for determine whether to perform starting assistance when starting the vehicle; a boost assistance determining device (S1307, S1310) for determining whether to perform boost assistance when in a gear-shift action; and a normal assistance determining device (S1124, S1135) for making the determination when the vehicle accelerates in a situation other than when starting the vehicle or in the gear-shift action. The first assistance amount determining device comprises a normal assistance amount determining device (S1029) for determining a normal assistance amount when the normal assistance determining device determines to perform the assisting function. The second assistance amount determining device comprises: a starting assistance amount determining device (S1274, S1276, S1277) for determining a starting assistance amount when the starting assistance determining device determines to perform the assist; and a boost assistance amount determining device (S1338) for determining a boost assistance amount when the boost assistance determining device determines to perform the assist. The assistance control device comprises: an assistance amount selector (S1005) for selecting one of the starting assistance amount (STRASTF), the boost assistance amount (SCRASTF), and the normal assistance amount (ACCASTF), when the assistance determining device determines at least one of the starting assist, the boost assist, and the normal assist; and an assistance controller for driving the motor to assist the output from the engine, based on the selected assistance amount.
In a fifth aspect of the present invention, the assistance amount selector selects the greatest one of the starting assistance amount, the boost assistance amount, and the normal assistance amount.
When the driver wishes to accelerates the vehicle, one of the starting assistance determining device, the boost assistance determining device, and the normal assistance determining device appropriately detects the intention of the driver. The starting assistance amount determining device, the boost assistance amount determining device, and the normal assistance amount determining device calculate the assistance amounts. The assistance amount selector selects the greatest one of the assistance amounts. Thus, the assistance can be performed effectively.
In a sixth aspect of the present invention, the starting assistance determining device determines whether to perform the assist, based on at least an engine speed (NE) and a vehicle speed (VP).
Thus, the presence or absence of the driver""s intention to accelerate the vehicle can be accurately detected when starting the vehicle.
In a seventh aspect of the present invention, the starting assistance determining device determines whether to perform the assist, based on at least one of a throttle opening state (THEM) and an air intake passage pressure (PBG).
Thus, the degree of the acceleration requested by the driver can be detected when starting the vehicle.
In an eighth aspect of the present invention, the boost assistance determining device determines whether to perform the assist, based on a throttle opening state (THEM) and a variation (DTHEM) in the throttle opening state.
Thus, the presence or absence of the driver""s intention to accelerate the vehicle can be accurately detected when in a shift-change action.
In a ninth aspect of the present invention, the boost assistance amount determining device sets the assistance amount, based on at least an engine speed (NEB).
Thus, the presence or absence of the driver""s intention to accelerate the vehicle can be accurately detected when in a shift-change action.